Transfer imaging system

ABSTRACT

A transfer imaging system is disclosed wherein images are formed by image-wise exposing a layer comprising a chromogenic material and pressure rupturable capsules containing, as an internal phase, a photosensitive composition. In a preferred embodiment, the chromogenic material is encapsulated with the photosensitive composition. Upon exposure and capsule rupture the chromogenic material is image-wise transferrable to a developer or copy sheet where the chromogenic material reacts with a developer to form an image. Preferred systems are sensitive to U.V. or blue light in the wavelength range of 380 to 480 nm.

This is a continuation of application Ser. No. 320,356, filed Nov. 12,1981, now U.S. Pat. No. 4,399,209.

BACKGROUND OF THE INVENTION

The present invention relates to an imaging system and more particularlyto an office based system which is suitable for making photocopies. Inaccordance with the invention, images are formed by image-wise exposinga composition comprising a chromogenic material and photosensitiveencapsulate to actinic radiation and rupturing the capsules in thepresence of a developer whereby a patterned reaction between thechromogenic material and developer is obtained which produces an image.This application specifically addresses transfer systems in which thecapsules are ruptured in contact with a developer sheet to whichchromogenic material is transferred for the patterned image-formingreaction.

Imaging systems based on photosensitive encapsulates are known. Berman,U.S. Pat. No. 3,219,446 discloses a transfer imaging process in whichazo-blue-"B" black dye is encapsulated with a cross-linkable polymer ora polymerizable monomer as a fluid-droplet containing film or a fluiddroplet containing microcapsules. As described, the Berman imagingsystem is a transfer system which relies upon selectively transferringthe encapsulated dye to a copy sheet in correspondence with the image.Imaging is accomplished by image-wise exposing a layer of theencapsulate to electromagnetic radiation to cross-link the polymer,causing the liquid in the exposed capsules to assume a rigid conditionand not transfer to a copy sheet. Dye transfer is limited to theunexposed areas of the encapsulate containing layer.

Phillips, U.S. Pat. No. 3,700,439 discloses a photocopy process whereinMichler's ketone is encapsulated in a conventional manner and providedas a layer on a support. Michler's ketone itself is not a color former,but patterned irradition of the ketone containing capsules produces alatent image of colorless, acid-colorable, dye precursor from the ketonesuch that upon contact with an acid developer such as acid clay avisible image is obtained. Phillips discloses both a system wherein theexposed imaging sheet is calendered face-to-face with an acid-coatedreceiving sheet to form images and a system wherein the acid developeris on the same surface as the capsule coating so that after rupturingthe capsules on the imaging sheet there is development without transfer.

Berman et al, U.S. Pat. No. 3,072,481 discloses another type ofencapsulated light sensitive element which utilizes a light-sensitivematerial which is readily converted to a colored form when carried in aliquid vehicle but which is insensitive to light when solid. Byencapsulating such a material with a volatile solvent, image-wiseexposing a layer of the encapsulate and rupturing the capsules toevaporate the solvent, an image is obtained and fixed.

Forris, U.S. Pat. No. 3,001,873, discloses a more complex system whereinthe walls of capsules containing a solid dye are photosensitized suchthat patterned exposure renders the capsules unswellable. By wetting thesheet to swell the unexposed capsules and heating, the dye isimmobilized in the unexposed areas. Thereafter, by rupturing thecapsules in contact with a receiving sheet there is an image-wisetransfer of the dye from the exposed areas only.

While image-forming techniques such as these have been know, for variousreasons, they have not matured into commercial photocopy systems.Furthermore, the potential of these systems to afford a low cost imagingsystem has not been realized.

SUMMARY OF THE INVENTION

Thus, a principal object of the present invention is to provide animaging system in which images are formed by image-wise exposing aphotosensitive encapsulate to actinic radiation and rupturing thecapsules in the presence of a developer such that there is a patternedreaction of a chromogenic material, present in the encapsulate orco-deposited on a support with the encapsulate, and the developer whichyields an image of the original.

Another object of the present invention is to provide an imaging systembased on a photosensitive encapsulate which provides images with highresolution and good tonal qualities.

Still another object of the present invention is to provide a dryphotocopy system which is affordable and does not require expensive andsophisticated machinery for exposure and processing.

A specific object of the present invention is to provide a transferimaging system in which an image-wise exposed imaging sheet bearing thephotosensitive encapsulate is placed in contact with a developer or copysheet and the capsules are ruptured such that chromogenic materialpattern-wise transfers to the developer sheet and reacts to form animage.

Another object of the present invention is to provide an imaging systemwhich is useful in transmission and reflected light imaging and hencecan be utilized in photocopying printed documents and other materials.

Another object of the present invention is to provide an imaging sheetcarrying a photosensitive encapsulate wherein the encapsulate comprisesa chromogenic material and a photosensitive composition.

Another more particular object of the present invention is to provide animaging paper which is sensitive to blue light (380 to 480 nm), andwhich incorporates a fugitive yellow dye such that said system can behandled in room light for sufficiently short periods of time to loadsaid paper in an exposure apparatus.

A still further object of the present invention is to provide an imagingprocess wherein images are formed by exposing a layer of aphotosensitive encapsulate preferably containing a chromogenic materialto actinic radiation, and rupturing the capsule in the presence of adeveloper.

These and other objects are attained in the present invention which in aspecific embodiment relates to a transfer imaging system basicallyhaving:

an imaging sheet having a first substrate,

a chromogenic material,

a photosensitive composition,

a coating containing said chromogenic material and said photosensitivecomposition on one surface of said first substrate,

said photosensitive composition being encapsulated in pressurerupturable capsules, as an internal phase, and

a developer sheet comprising a second substrate and a developer materialwhich is capable of reacting with the chromogenic material to form a animage on one surface of said second substrate upon transfer of saidchromogenic material thereto.

Herein, the term "encapsulated" refers to both so-called resindispersion or open phase systems in which the internal phase containingthe chromogenic material is dispersed as droplets throughout adispersing medium and systems in which the capsule is formed with adiscrete capsular wall, the latter encapsulation typically being in theform of microcapsules. "Pressure rupturable capsules" are, accordingly,considered to exist in either of these "encapsulated" systems.Furthermore, while the capsules are described herein as "pressurerupturable" means other than pressure may be used to rupture them.

In accordance with the present invention images are formed by exposing acoated composition containing the chromogenic material and theencapsulated photosensitive composition to actinic radiation andrupturing the capsules in the presence of a developer. The inventionsystem is designed such that when these steps are carried out, theimage-forming reaction between the chromogenic material and thedeveloper discriminately occurs in the exposed or unexposed areas andproduces a detectable image. In the case of a transfer imaging system,this is accomplished by image-wise photochemically controlling whetherthe chromogenic material can transfer from the imaging sheet to thedeveloper sheet. By "image-wise" it is meant that upon exposure andtransfer the chromogenic material and the developer react to form apositive or negative image of the original.

In accordance with the principal embodiment of the invention, thechromogenic material is encapsulated with a photosensitive composition.In general, the photosensitive composition can be described as onehaving a viscosity which changes upon exposure to actinic radiation suchthat upon exposure there is a change in the viscosity of the internalphase in the exposed areas which image-wise determines whether thechromogenic material is accessible to the developer. The photosensitivecomposition may be radiation curable composition which, upon exposure tolight, increases in viscosity and immobilizes the chromogenic material,thereby preventing it from transfering to the developer sheet andreacting with the developer material entirely or in proportion to thetonal depth of the image in the exposed areas. [The term "curable" asused herein is not limited to materials which are cross-linked, but isopen to materials which are simply polymerized.] In another case thechromogenic material is encapsulated with a substance which isdepolymerized or otherwise decreased in molecular weight upon exposure,resulting in a decrease in viscosity which renders the chromogenicmaterial accessible (transferable) to the developer in the exposedareas.

It will be evident that in the former case the system is a positiveworking system, whereas in the latter case it is a negative-workingsystem. Using a radiation curable material, when the internal phasecontains the chromogenic material, it is rendered inaccessible to thedeveloper in the exposed areas, thereby preventing the formation of animage in those areas. More particularly, the chromogenic material isimmobilized in the cured matrix of the photosensitive composition suchthat it cannot transfer to the developer sheet and react to form animage. In the unexposed areas, which in reflection imaging correspond tothe printed areas of printed documents, the internal phase remainsliquid and the chromogenic material can react with the developer to forma positive image. In a negative-working system, the photosensitivecomposition in a chromogenic material containing encapsulate is viscousand upon exposure it liquefies so that the chromogenic material istransferable to the developer sheet. Thus, in this system, exposurerenders the chromogenic material accessible to the developer, thechromogenic material being inherently immobilized in the unexposedmaterial.

The chromogenic material is not necessarily encapsulated with thephotosensitive composition although this is a preferred means forcarrying out the present invention. The chromogenic material may beco-deposited on the supporting substrated with the encapsulatedphotosensitive composition or contained in the capsular wall such thatupon capsule rupture the chromogenic material is dissolved and carriedto the developer material in a discriminate manner. Hence, thephotosensitive composition may be encapsulated with a solvent for thechromogenic material or the unpolymerized monomer may dissolve thechromogenic material such that as a result of the exposure, the accessbetween the developer and the chromogenic material is controlled asdescribed herein.

It should be apparent that the system does not necessarily require agiven capsule to completely release or completely retain its chromogenicencapsulate as long as there is a difference in the amount ofchromogenic material transferring or migrating to the developer in theexposed versus the unexposed areas. Indeed, the invention producesimages having tonal quality superior to that obtained in mostconventional photocopy systems. One reason for the tonal quality of theimages obtained in accordance with the invention is that the amount ofchromogenic material released from a given area of a microcapsule coatedsheet depends on the degree of exposure of the internal phase of thecapsules in that area. Furthermore, it is also not clear whether theamount of chromogenic material transferred is determined by differentialcapsule rupture (image versus non-image areas) in the invention. Underone theory all of the capsules (in both image and non-image areas) areuniformly ruptured and they transfer chromogenic material in proportionto the viscosity of the internal phase in that area or at that point ofthe image. Under another theory the tonal range of the images are formedby a matrix of ruptured and unruptured capsules. In actuality, acombination of both theories may occur. Regardless of the theory, uponrupture of the capsules there is patterned release and immobilization ofthe encapsulate according to the exposure and which it has been foundcorresponds to the degree of exposure such that tonal gradation isobtained.

The imaging system of the present invention can be made sensitive tovarious forms of radiation, and as such, the term "actinic radiation" asused herein includes the full spectra of electromagnetic radiationincluding ultraviolet, infrared, the entire visible spectrum, as well asX-ray and ion beam radiation. The preferred forms of actinic radiationare ultraviolet radiation and visible light having a wavelength of 190to 800 nm and a most preferred range of 380 to 480 nm (blue light).

Ultraviolet sensitive systems are desirable because they can be handledin room light for sufficiently long periods of time to permit thephotosensitive material to be removed from the light-shielding packagingin which it is stored and installed in an exposure apparatus withoutincorporating auxiliary shielding elements into the imaging sheet. Thedisadvantage to ultraviolet sensitivity is that many documents areprinted on papers which include optical brighteners or TiO₂ which absorbultraviolet radiation and, therefore, it is difficult to use ultravioletradiation to make copies of such documents by reflection imaging.

Blue light sensitivity is advantageous because it avoids the opticalbrightener problem and it is a simple matter to build temporaryscreening means into the system for room light handleability.

Where the imaging system is sensitive to blue or visible light, theimaging sheet may be constructed with means to temporarily shield thesystem from visible light to permit room-light handleability. Forexample, when the imaging system is sensitive to blue light having awavelength of 380 to 480 nm, imaging sheets may be constructed with afilter layer which incorporates a fugitive yellow dye. The shieldingeffect of the dye need not be complete, it is sufficient if the imagingsheet can be handled in room light for only the short period of timerequired to install it in the exposure apparatus. Once installed in theexposure apparatus, the fugitive dye is deactivated, for example, bythermal bleaching, so that the system can be exposed by blue lightirradiation in the exposure apparatus. Room light handleability can alsobe achieved by controlling the sensitivity level of the composition suchthat exposure to room light of short duration does not interfere withimage formation which is accomplished using more intense radiation.

The imaging system of the present invention may be embodied in aself-contained copy sheet in which the encapsulated chromogenic materialand the developer material are co-deposited on one surface of a singlesubstrate as one layer or as two contiguous layers, or in a 2-plytransfer element in which the developer material is coated on a separatesubstrate as a developer or copy sheet. The former system is the subjectof commonly assigned U.S. application Ser. No. 320,643, now U.S. Pat.No. 4,440,846 filed on even date herewith in the names of the sameinventors. Both systems operate by photographic control of the accessbetween the chromogenic material and the developer as previouslydescribed. In the self-contained imaging system, following capsulerupture, the chromogenic material and the developer are able to react toform a visible image in the exposed or the unexposed areas (depending onthe nature of the viscosity change produced by exposure). Gradualdevelopment of the visible image is observed following exposure andcapsule rupture as the chromogenic material and developer migrate, mixand react on the face of the sheet.

The transfer system addressed herein, on the other hand, operates byselective transfer of the chromogenic material from a transfer orimaging sheet to a developer or copy sheet containing the developermaterial. Depending on the nature of the photosensitive systemencapsulated with the chromogenic material, the chromogenic materialmigrates from the exposed or unexposed areas of the imaging sheet to thedeveloper sheet where it reacts with the developer and forms a visibleimage. For example, where a radiation curable material such astrimethylol propane triacrylate together with a photoinitiator,constitute the photosensitive composition, upon exposure the triacrylateis polymerized into a viscous mass. Thus, in the exposed areas thechromogenic material is sufficiently immobilized that it cannot transferto the developer sheet and form color by reaction with the developermaterial. In the unexposed areas, which correspond to the image, theinternal phase remains liquid such that the chromogenic material can betransferred to the developer sheet where it reacts with the developerand forms a positive image.

In the most typical embodiment, capsule rupture is effected by theapplication of pressure to the imaging sheet alone (in the case of aself-contained system) or in contact with a developer sheet (aspreferred in a transfer system). Alternative means of capsule rupturecan also be used. For example, systems, are envisioned in which thecapsules are ruptured ultrasonically, thermally, or by solvent. Aspreviously noted, the invention is applicable to open phase systems aswell as systems involving a discrete capsular wall and the method ofrupture may depend on the system employed, thermal rupture being a morelikely means in conjunction with an open phase system. Due to thevolatility of the internal phase, in most instances the capsules areruptured in contact with the developer sheet in transfer elements.

Various materials can be used as the chromogenic material and thedeveloper material in the present invention. In this regard, many of thematerials conventionally employed in so-called carbonless paper are alsosuitable for use in the present invention. In the most typical case, thechromogenic material is an electron donating compound and the developeris an electron accepting compound. Preferably, in their unreacted state,these materials are colorless or they are non-absorbing as to theexposure radiation. It is possible to interchange the chromogenicmaterial and the developer using an electron accepting compound inconjunction with the photosensitive composition in the internal phaseand using an electron donating compound as the developer material. Inmost cases the chromogenic material is a dye precursor and preferably ablack dye precursor, although a variety of other color precursors arealso disclosed below for use in the invention.

In the preferred case, the internal phase contains a radiation curablematerial. The radiation curable materials used in one embodiment of theinvention are preferably free radical addition polymerizable materials.Preferred materials are ethylenically unsaturated compounds and, moreparticularly, compounds having two or more ethylenically unsaturatedterminal groups.

The imaging system of the present invention is quite versatile. It isuseful in making copies from printed documents, duplicating blue printsand other line drawings, among other utilities. The invention system canbe used to produce monochromatic copies in black or any other color.Some of its principal advantages are the superior tonal quality of theimages that are obtained and the fact that imaging can be accomplishedusing a fairly simple exposure apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration in cross-section of an imaging sheetand a transfer sheet constructed in accordance with invention;

FIG. 2 is a schematic illustration of exposure of the imaging sheet; and

FIG. 3 is a schematic illustration of transfer development.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates one embodiment of the imaging system of the presentinvention. Therein an imaging sheet 10 is shown comprising a substrate12 coated with a layer of microcapsules 14. The microcapsules are filledwith an internal phase 16 containing a chromogenic material and aphotosensitive composition. In actuality, the microcapsules 14 are notvisible to the unaided eye. Associated with the imaging sheet 10 is adeveloper sheet 19 comprising a substrate 20 and a layer 21 of adeveloper material. Again, in actuality, the developer material is notseen by the unaided eye as a separate layer.

Exposure of the imaging sheet 10 by transmission imaging is shown inFIG. 2 wherein a source of radiant energy 22 is positioned above thesurface of the imaging sheet 10 with a mask 24 therebetween. In thisillustration the substrate 12 is opaque and the photosensitive materialis a positive working resin curable material. Irradiation of the exposedareas 28 causes the radiation curable material in the internal phase 16to polymerize, thereby gelling, solidifying or otherwise immobilizingthe chromogenic material. To simplify the illustration internal phase16' in the exposed areas 28 is shown as a solid whereas the internalphase 16 remains liquid in the unexposed areas 26. Those skilled in theart will appreciate that while transmission imaging has been used toillustrate the invention for its simplicity, reflected light imaging isthe preferred means of copying printed documents.

Image formation or development is shown in FIG. 3 wherein the nowexposed imaging sheet 10 becomes a transfer sheet and is placed with itsmicrocapsule layer 14 in face to face contact with the developermaterial 21 of developer sheet 19 and a pressure P is uniformly appliedacross the sheets. For simplification, the pressure is shown asrupturing the microcapsules in the unexposed areas 26 and not rupturingthe capsules in the exposed areas 28. This is in accordance with onetheory of operation which holds that in the exposed areas the internalphase is hardened to such an extent that the microcapsules can no longerbe ruptured. There is another theory, however, which holds that all thecapsules are ruptured but the chromogenic material is immobilized by theincreased viscosity which results in the internal phase 16' in theexposed areas 28 upon exposure. In actuality all or a portion of thecapsules may also be ruptured in exposed areas 28. Typically, thecapsules are ruptured by passing the imaging sheet 10 and the developersheet 20 together through a pressure nip. This causes the internal phase16 from the unexposed areas 26 to transfer to the developer sheet 19, asshown schematically by arrows in FIG. 3. Upon transfer of the internalphase 16 to the developer sheet 19, the chromogenic material reacts withthe developer layer 21 and forms an image 30 on the developer sheet. Itshould be apparent that while the radiation curable material provides apositive working imaging sheet in that the exposed areas arenon-transferable and the unexposed areas are transferable, thetransfered image 30 is reversed (right-left) compared to the latentimage in the imaging sheet 10 but is a positive duplicate of the mask24. This presents no problem if the radiation passes through an imagedtransparency or mask 24 as shown in FIG. 2. But ordinary copyinginvolves use of opaque documents which can not be used in this manner.Thus, a reflection or optical projection system is used for copyingordinary documents as is well known in other photocopying technologies.

The operational center of the imaging system of the present invention isthe encapsulate or internal phase of the coating composition. Inaccordance with the invention, the internal phase comprises aphotosensitive composition. Typically, the photosensitive compositionincludes a photoinitiator and a substance which undergoes a change inviscosity upon exposure to light in the presence of the photoinitiator.That substance may be a monomer, dimer, or oligomer which is polymerizedto a higher molecular weight compound or it may be a polymer which iscross-linked. Alternatively it may be a compound which is depolymerizedor otherwise decomposed upon exposure.

In the most typical case, the photosensitive composition includes aradiation curable material. The radiation curable materials useful inthe practice of the present invention are preferably materials curableby free radical initiated chain propagated addition polymerization orionic polymerization. Substantially any photopolymerizable compositionwhich can be encapsulated and which does not interfere with theimage-forming capability of the chromogenic material can be used. Thesematerials may be inherently sensitive to the actinic radiation, in whichcase they may be hardened without a photoinitiator but usually they arematerials which are curable in the presence of a photoinitiator.Furthermore, while in the most typical case, the radiation-curablematerials are monomers which undergo an increase in viscosity as aresult of polymerization, they may also be oligomers, prepolymers, orpolymers which undergo cross-linking upon exposure. In addition to freeradical polymerizable materials they may also be materials which arepolymerized or cross-linked ionically, e.g., by generation of a Lewisacid.

Representative radiation curable materials are ethylenically unsaturatedorganic compounds. These compounds contain at least one terminalethylenic group per molecule. Typically they are liquid and can alsodouble as a carrier oil for the chromogenic material in the internalphase.

A preferred group of radiation curable materials is ethylenicallyunsaturated compounds having two or more terminal ethylenic groups permolecule. Representative examples of these compounds includeethylenically unsaturated acid esters of polyhydric alcohols such astrimethylol propane triacrylate.

Another preferred radiation curable substance is an acrylate prepolymerderived from the partial reaction of pentaerythritol with acrylic acidor acrylic acid esters. Radiation curable compositions based on suchprepolymers having an acrylate functionality of between approximatelytwo and three are available commercially in two-package system radiationcurable compositions from the Richardson Company, Melrose Park, Ill.,such as RL-1482 and RL-1483 which are recommended to be mixed togetherto form a radiation curable clear varnish in a ratio of 4.4 parts ofRL-1482 to 1 part RL-1483.

Isocyanate modified acrylate, methacrylic and itaconic acid esters ofpolyhydric alcohols as disclosed in U.S. Pat. Nos. 3,783,151; 3,759,809and 3,825,479 all to Carlick et al which are specifically incorporatedby references, are also useful. Radiation curable compositions based onthese isocyanate modified esters and including reactive diluents such astetraethylene glycol diacrylate as well as photoinitiators such aschlorinated resins, chlorinated paraffins and amine photoinitiationsynergists are commercially available as overprint varnishes from SunChemical Corporation, Carlstat, N.J., under the trade name of Suncureresins.

Another class of curable materials useful in the present invention arefound in radiation curable inks as the photosensitive component such asa mixture of a pentaerythritol acrylate and hologenated aromatic,alicyclic or aliphatic photoinitiator as disclosed in U.S. Pat. No.3,661,614 to Bessemir et al, which is also incorporated by reference.Still another type of radiation curable material is halogenated resinswhich can be cross-linked by ultraviolet radiation.

Some typical examples of radiation de-polymerizable materials useful inother embodiments of the invention are 3-oximino-2-butanone methacrylatewhich undergoes main chain scission upon U.V. exposure and poly 4'-alkylacylo-phenones. See Reichmanis, E.; Am. Chem. Soc. Div. Org. Coat.Plast. Chem. Prepr. 1980, 43, 243-251 and Lukac, I.; Chmela S., Int.Conf. on Modif. Polym. 5th. Bratislave, Czech. July 3-6, 1979,I.U.P.A.C. Oxford, England 1979, 1, 176-182.

The radiation curable or depolymerizable material usually makes up themajority of the internal phase. A radiation curable material must bepresent in an amount sufficient to immobilize the chromogenic materialupon exposure. With a depolymerizable material, on the other hand, theinternal phase must be constituted such that the chromogenic material isimmobilized prior to exposure but is released after exposure and capsulerupture. Typically these materials constitute 40 to 99 wt % of theinternal phase (based on the weight of the oil solution containing thechromogen, the photosensitive composition and the carrier oil whenpresent). In some embodiments, it has been found desirable to dilute thephotosensitive composition with a carrier oil to improve half-tonegradation. In these cases a carrier oil is present in the amountsdisclosed below and the aforesaid materials make up to 40 wt % of theinternal phase.

Those skilled in the art will appreciate that various photoinitiatorscan be selected for use in the present invention depending on thesensitivity that is desired in accordance with the present invention.These compounds absorb the exposure radiation and generate a freeradical alone or in conjunction with a sensitizer. Conventionally, thereare homolytic photoinitiators which cleave to form two radicals andinitiators which radiation converts to an active species which generatesa radical by abstracting a hydrogen from a hydrogen donor. There arealso initiators which complex with a sensitizer to produce a freeradical generating species and initiators which otherwise generateradicals in the presence of a sensitizer. Both types can be used in thepresent invention. If the system relies upon ionic polymerization to tieup the chromogen, the initiator may be the anion or cation generatingtype depending on the nature of the polymerization. Where, for example,ultraviolet sensitivity is desired, as in the case of directtransmission imaging using ultraviolet light, suitable photoinitiatorsinclude α-alkoxy phenyl ketones, O-acylated α-oximinoketones, polycylicquinones, benzophenones and substituted benzophenones, xanthones,thioxanthones, halogenated compounds such as chlorosulfonyl andchloromethyl polynuclear aromatic compounds, chlorosulfonyl andchloromethyl heterocyclic compounds, chlorosulfonyl and chloromethylbenzophenones and fluorenones, haloalkanes, α-haloα-phenylacetophenones; photoreducible dye-reducing agent redox couples,halogenated paraffins (e.g., brominated or chlorinated paraffin) andbenzoin alkyl ethers.

The following compounds may be useful as photoinitiators in the presentinvention:

α-alkoxyphenyl ketones of the formula I ##STR1## where R¹ is a C(1-4)alkyl group (e.g., methyl, ethyl, n-propyl, i-propyl, t-butyl, etc.), R²is a phenyl group or a substituted phenyl group wherein said substituentis as defined for X below, R³ is hydrogen or a C(1-4) alkyl group, and Xis hydrogen, an alkoxy group having 1 to 4 carbon atoms (e.g., methoxy,ethoxy, propyloxy, etc.), a dialkylamino group wherein said alkyl groupcontains 1 to 4 carbon atoms, a nitro group, a nitroso group, a cyanogroup, a mercapto group, chlorine, bromine or iodine, an alkyl grouphaving 1 to 4 carbon atoms, an alkenyl group having 1 to 4 carbon atoms,an acyl group, a phenyl group, or a carboalkoxy group having 2 to 5carbon atoms;

an α,α, dialkoxyphenyl ketone of the formula II ##STR2## where R¹, R²and X are defined as in formula I;

1-phenyl-1,2-propanedione-2-O-benzoyloxime,

9,10-phenanthraquinone,

9,10-anthraquinone,

a benzophenone of the formula III ##STR3## where X' is hydrogen, anamino group, or a dialkylamino group, the alkyl group having 1 to 4carbon atoms, and Y is hydrogen, an alkyl group having 1 to 4 carbonatoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyl grouphaving 1 to 4 carbon atoms, a phenyl group a substituted phenyl group, adialkylamino group, a nitro group, a nitroso group, a cyano group, amercapto group, chlorine, bromine, iodine, or an acyl group;

xanthone, a chloroxanthone, a chloromethyl xanthone, a chlorosulfonylxanthone,

thioxanthone, a chlorothioxanthone, a chloromethyl thioxanthone, achlorosulfonyl thioxanthone,

chloromethylnaphthalene,

chlorosulfonyl naphthalene,

chloromethyl anthracene,

chlorosulfonyl anthracene,

chloromethyl benzoxazole,

chloromethyl benzothiazole,

chloromethyl benzimidazole,

chlorosulfonyl benzoxazole,,

chlorosulfonyl benzothiazole,

chlorosulfonyl benzimidazole,

a chloromethyl quinoline,

a chlorosulfonyl quinoline,

a chloromethyl benzophenone,

a chlorosulfonyl benzophenone,

a chloromethyl fluorenone,

a chlorosulfony fluorenone,

carbon tetrabromide,

benzoin methyl ether,

benzoin ethyl ether,

desyl chloride,

desyl amine,

methylene blue/ascorbic acid,

chlorinated aliphatic hydrocarbons and combinations thereof.

The sensitivity among these compounds can be shifted by addingsubstituents such that the compounds generate radicals when exposed tothe desired radiation wavelength. For visible (blue) light sensitivity,the aforementioned photoinitiators may be combined with a sensitizersuch as Michler's ketone or an anologous dialkylamino benzophenonethereof, a substituted coumarin, a linear polyene (e.g., transB-carotene) or sensitizing dye, e.g., a yellow dye.

For ultraviolet sensitivity a preferred photoinitiator-sensitizer is acombination of Michler's ketone and benzoin methyl ether (preferredratio 2:5).

The photoinitiator is present in the internal phase in an amountsufficient to initiate polymerization or cross-linking within a shortexposure time. Using benzoin methyl ether as an example, thisphotoinitiator is typically present in an amount of up to 10% based onan amount of radiation curable material in the internal phase.Naturally, the amount varies depending on the nature of the othercomponents of the photosensitive composition. Those skilled in the artcan readily determine amounts suitable for the desired exposureproperties. An instantaneous system would be desirable, i.e., one whichwill provide an image with less than 0.5 to 1 second exposure, however,exposure times ranging from 0.5 to up to 1 minute are sometimesrequired. The actual exposure time will also depend on a number ofvariables such as coat weight, coat thickness, the radiation curablesubstance (rate of photopolymerization), the type and source ofradiation, the radiation intensity and its distance from the sheet.

It is also possible to reduce the exposure time by incorporating ascattering agent in the capsule layer. A scattering agent increases themean free path and thereby intensifies exposure. One such scatteringagent that can be used in the present invention is magnesium dioxide.

The chromogenic materials used in the present invention are preferrablyoil soluble color formers which will produce a color upon reaction witha developer material in the presence of a carrier oil. Substantially anyof the chromogenic materials conventionally used in carbonless paper canbe used in the present invention. In general, these materials arecolorless electron donating type compounds. Representative examples ofsuch color formers include substantially colorless compounds having intheir partial skeleton a lactone, a lactam, a sulfone, a spiropyran, anester or an amido structure. Specifically, there are triarylmethanecompounds, bisphenylmethane compounds, xanthene compounds, thiazinecompounds, spiropyran compounds and the like. Typical examples of theminclude Crystal Violet lactone, benzoyl leuco methylene blue, MalachiteGreen Lactone,

p-nitrobenzoyl leuco methylene blue,

3-dialkylamino-7-dialkylamino-fluoran,

3-methyl-2,2'-spirobi(benzo-f-chrome),

3,3-bis(p-dimethylaminophenyl)phthalide,

3-(p-dimethylaminophenyl)-3-(1,2dimethylindole-3-yl)phthalide,3-(p-dimethylaminophenyl)-3-(2-methylindole-3-yl)phthalide,3-(p-dimethylaminophenyl)-3-(2-phenylindole-3-yl)phthalide,

3,3-bis(1,2-dimethylindole-3-yl)-5-dimethylaminophthalide,3,3-bis-(1,2-dimethylindole-3-yl)6-dimethylaminophthalide,

3,3-bis-(9-ethylcarbazole-3-yl)-5-dimethylaminophthalide,3,3-bis(2-phenylindole-3-yl)-5-dimethylaminophthalide,3-p-dimethylaminophenyl-3-(1-methylpyrrole-2-yl)-6-dimethylaminophthalide,

4,4'-bis-dimethylaminobenzhydrin benzyl ether,

N-halophenyl leuco Auramine, N-2,4,5-trichlorophenyl leuco Auramine,Rhodamine-B-anilinolactam,

Rhodamine-(p-nitroanilino)lactam,

Rhodamine-B-(p-chloroanilino)lactam,

3-dimethylamino-6-methoxyfluoran,

3-diethylamino-7-methoxyfluoran,

3-diethylamino-7-chloro-6-methylfluroan,

3-diethylamino-6-methyl-7-anilinofluoran,

3-diethylamino-7-(acetylmethylamino)fluoran,

3-diethylamino-7-(dibenzylamino)fluoran,

3-diethylamino-7-(methylbenzylamino)fluoran,

3-diethylamino-7-(chloroethylmethylamino)fluoran,

3-diethylamino-7-(diethylamino)fluoran,

3-methyl-spiro-dinaphthopyran,

3-ethyl-spiro-dinaphthopryan,

3,3'-dichloro-spiro-dinaphthopyran,

3-benzyl-spiro-dinaphthoypyran,

3-methyl-naphtho-(3-methoxybenzo)-spirpyran,

3-propyl-spirodibenzoidipyran, etc.

Mixtures of these color precursors can be used if desired. Also usefulin the present invention are the fluoran color formers disclosed in U.S.Pat. No. 3,920,510, which is incorporated by reference.

The present invention, however, is not limited to the use of theaforementioned color precursors as chromogenic materials. In addition,organic chemicals which are capable of reacting with heavy metal saltsto give colored metal complexes, chelates or salts can be adapted foruse in this invention.

Substantially any color forming material which can be encapsulated andwhich will react with a developer material to form an image can be usedin the present invention. Furthermore, it is not necessary to maintainthe conventional distinction between color formers and color developersin the invention system. That is, in some embodiments, the chromogenicmaterial may be what is commonly referred to as a color developerprovided it does not absorb in the exposure radiation range so as tointerfere with imaging.

In addition to the chromogenic material and the photosensitive material,the internal phase of the present invention may also include a carrieroil. Preferred carrier oils are weakly polar solvents having boilingpoints above 170° C. and preferably in the range of 180° C. to 300° C.The carrier oils used in the present invention are typically thoseconventionally used in carbonless paper manufacture. These oils aregenerally characterized by their ability to dissolve Crystal VioletLactone in a concentration of 0.5 wt % or more. However, a carrier oilis not always necessary. Whether a carrier oil should be used willdepend on the solubility of the chromogenic material in thephotosensitive composition before exposure, the nature of thechromogenic material and the viscosity of the characteristics of theinternal phase. When present, examples of carrier oils are alkylatedbiphenyls (e.g., monoisopropylbiphenyl), polychlorinated biphenyls,castor oil, mineral oil, deodorized kerosense, naphthenic mineral oils,dibutyl phthalate, dibutyl fumerate, brominated paraffin and mixturesthereof. Alkylated biphenyls are generally less toxic and preferred.

The presence of a carrier oil affects and can be used to control thetonal quality of the images obtained. While tonal quality (half-tonegradation) is not critical when copying printed documents, it is animportant factor in faithfully reproducing pictoral images. Initialstudies show that where trimethylol propane triacrylate is used in theradiation curable material, 20% of a carrier oil such as brominatedparaffin improves tonal qualities.

In accordance with the invention, the chromogenic material isincorporated in the internal phase in an amount sufficient to produce avisible image of the desired density upon reaction with the developer.In general, these amounts range from approximately 0.5 to about 20.0percent based on the weight of the internal phase solution (e.g.,monomer or monomer and oil) containing the chromogen. A preferred rangeis from about 2 percent to about 7 percent. The amount of thechromogenic material required to obtain suitable images depends on thenature of the chromogen, the nature of the internal phase, and the typeof imaging system. Typically less chromogenic material is used in theinternal phase of a self-contained imaging system in comparison to atransfer system. This is because the developer material is co-depositedon a common substrate with the chromogenic encapsulate and there is atendency for the chromogenic material to diffuse through the capsulewall and react with the developer material during storage and becausethere is no inherent loss in transfer. One means of preventing undesiredcoloration in a self-contained sheet is to reduce the amount of thechromogenic material in the internal phase. Another means is toincorporate color suppressants with the chromogenic material.

Typically a transfer imaging sheet contains 6 percent chromogenicmaterial in the internal phase whereas self-contained imaging sheetshave been formed using 1.5 to 3 percent of chromogenic material.

As indicated above, the imaging systems of the present invention may beformulated such that they are sensitive to any of ultraviolet, infrared,X-ray, ion beam, and visible radiation. For room light handleability,ultraviolet sensitive imaging systems are preferred. Ultravioletsensitive imaging systems are suitable for recording images from acathode ray tube as well as in reproducing images from a transparent ortranslucent photomask. Both of these systems rely upon transmittedultraviolet radiation to expose the imaging system. It has been found,however, that ultraviolet sensitivity is generally not suitable when itis desired to reproduce a printed document by reflection imaging (e.g.,contact reflection imaging or optical projection imaging using reflectedlight). The reason for this is that the vast majority of printeddocuments are on papers containing optical brightening agents or TiO₂.These agents act as black dyes in an ultraviolet imaging system andabsorb the ultraviolet radiation. Hence the background and image areasare both ultraviolet absorbers and there is no image discrimination byreflection imaging.

In making copies of printed documents, it has been found desirable touse a blue-light sensitive material. Using a blue-light sensitivematerial, it is possible to make the system handleable in room light byincorporating in the system a fugitive yellow filter dye which isbleached or otherwise rendered inactive or removed from the imagingsystem prior to exposure. The yellow dye absorbs blue-light and preventsan imaging material in accordance with invention from being exposed, forexample, as it is removed from a light-shielded container and installedin an exposure apparatus. The fugitive dye may incorporated in theimaging system in a separate layer which overcoats the layer of theencapsulated chromogenic and photosensitive materials or the fugitivedye may be fixed in the wall of a discrete walled microcapsulate. Yellowfugitive dyes are well known in the art. The preferred dyes are thosewhich can be inactivated or removed from the imaging system with thegreatest ease. Using these dyes, the imaging material is heated in theexposure apparatus to a temperature at which the dye is bleached priorto exposure. Thereafter, the imaging material can be exposed by theapplication of light in the visible blue range. In addition to thermallybleachable fugitive dyes, the invention is also open to the use of dyeswhich are bleached by oxidation. Although, using these dyes, a liquidprocessing step would normally be required to bleach the dye.

An internal phase as described above can be encapsulated in aconventional manner. Oil soluble chromogenic materials have beenencapsulated in hydrophilic wall-forming materials such as gelatinwall-forming materials (see U.S. Pat. Nos. 2,730,456 and 2,800,457 toGreen et al) including gum arabic, polyvinyl alcohol,carboxymethyl-cellulose; resorcinol-formaldehye wall-formers (see U.S.Pat. No. 3,755,190 to Hart et al), isocyanate wall-formers (see U.S.Pat. No. 3,914,511 to Vassiliades) isocyanate-polyol wall-formers (seeU.S. Pat. No. 3,796,669 to Kiritani et al) ureaformaldehyde wall-formersand more particularly Urea-resorcinol-formaldehyde wall forms (in whicholeophilicity is enhanced by the addition of resorcinal) (see U.S. Pat.Nos. 4,001,140; 4,087,376 and 4,089,802 to Foris et al)melamine-formaldehyde resin and hydroxypropyl cellulose (see commonlyassigned U.S. Pat. No. 4,025,455 to Shackle). To the extent necessaryfor complete disclosure of those wall-forming materials, the abovementioned patents are specifically incorporated by reference.Microencapsulation has been accomplished by a variety of knowntechniques including coacervation, interfacial polymerization,polymerization of one or more monomers in an oil, as well as variousmelting, dispersing and cooling methods.

The capsule forming material used in a given imaging system is selectedbased on the photosensitive composition present in the encapsulate.Thus, the formed capsule wall must be transmissive to the exposureradiation. Of the above systems urea-resorcinol-formaldehyde and gelatincapsules are preferred.

The mean size of the capsules used in the present invention generallyranges from approximately 1 to 25 microns. As a general rule, imageresolution improves as the capsule size decreases with the caveat thatif the capsule size is too small, depending on the nature of thesubstrate on which the capsules are coated, the capsules may disappearin the pores or the fiber in the substrate, but even capsules as largeas 25 microns provide satisfactory resolution in the present invention.In the latter case, the incongruities in the substrate may screen thecapsules from exposure and thereby diminish image quality. They may alsofail to rupture upon the application of pressure. In view of theforegoing, it has been found that a preferred mean capsule size range isapproximately 3 to 15 microns and particularly approximately 3 to 10microns although, technically, the capsules can range in size up to thepoint that they are visible to the human eye.

Capsular coating compositions are prepared in a conventional manner inaccordance with the present invention. Since the photosensitiveencapsulate of the present invention is usually hydrophobic, thewall-forming constituents and the film forming binder should behydrophilic and soluble in an aqueous based liquid as is conventional informing capsule containing coating compositions. Otherwise in certainknown reverse system the aqueous phase may be dispersed in a hydrophobiccontinuous phase. The microcapsules used in the present invention can beprepared by the methods disclosed in the aforementioned U.S. patents orby similar methods. For example, an oil solution of the internal phasecomprising the chromogenic and photosensitive composition is dispersedin a continuous phase containing the wall-forming constituents, andmicroencapsulation is accomplished by, for example, coacervation orinterfacial polymerization, among others. Open phase systems can beprepared by dispersing the internal phase in a solution of polymericbinder and adjusting the viscosity of the dispersion for coating. Amonga wide variety of suitable binders are gelatin, polyvinyl, alcohol,polyacrylamide, acrylic latices etc.

Coating compositions so formulated are applied and dried on a continuousweb of paper. Any ordinary coating or printing technique can be used inmaking imaging sheets in accordance with the invention including suchmeans as roller or blade coating.

The coating compositions of this invention may contain any of thevarious additives known in the carbonless paper art to improve thehandling characteristics of the coated copy sheet such as a stiltmaterial (e.g., starch particles), silica particles to prevent speckingwhen a pressure nip is used for capsule rupture, etc.

In its principal embodiment, the imaging system of the present inventionis used to produce copies of printed documents, and, as such, thesubstrate upon which the coating composition is coated is paper. Thepaper may be a commercial impact raw stock, or a special grade papersuch as cast-coated paper and chrome rolled paper. The latter examplesare desirable when using very fine microcapsules, e.g., capsules rangingin size from approximately 1 to 5 microns, as the surface of thesepapers is smoother and the microcapsules are not as easily embedded inthe stock fibers. Transparent substrates such as polyethyleneterephthalate and translucent substrates can also be used in theinvention and have the advantage that the latent image formed in theimaging sheets need not be reversed for printing.

The developer material used in the present invention is a compound ormaterial capable of reacting with the chromogenic material to produce acolor image. In the most typical case, the developer material is anelectron accepting compound or a so-called color developer. In thebroadest sense, however, the term "developer material" as used hereinrefers to that half of the color-forming reactant combination which isnot encapsulated with the photosensitive composition. Hence, as statedbefore, compounds conventionally recognized as color developers can beencapsulated as the chromogenic material in the present invention, andcompounds conventionally recognized as color formers can be used outsidethe capsule in the invention system.

The developer materials used in the present invention are thoseconventionally employed in carbonless paper technology and are wellknown. Illustrative specific examples are clay minerals such as acidclay, active clay, attapulgite, etc.; organic acids such as tannic acid,gallic acid, propyl gallate, etc.; acid polymers such asphenol-formaldehyde resins, phenol acetylene condensation resins,condensates between an organic carboxylic acid having at least onehydroxy group and formaldehyde, etc.; metal salts or aromatic carboxylicacids such as zinc salicylate, tin salicylate, zinc 2-hydroxynaphthoate, zinc 3,5 di-tert butyl salicylate, oil soluble metal saltsof phenol-formaldehyde novolak resins (e.g., see U.S. Pat. Nos.3,672,935; 3,732,120 and 3,737,410) such as zinc modified oil solublephenol-formaldehyde resin as disclosed in U.S. Pat. No. 3,732,120), zinccarbonate etc. and mixtures thereof. Again, to the extent necessary forcomplete disclosure of these developer materials, the above notedpatents are specifically incorporated by reference.

When used in a developer sheet, the color developer may be mixed with abinder such as latex, polyvinyl alcohol, maleic anhydride-styrenecopolymer, starch and gum arabic. It is to be understood that allbinders well known as film-forming materials can be used in thiscapacity.

Imaging sheets embodying the invention imaging system can be exposedusing a fairly simple exposure apparatus. In its simplest form forreflection imaging, the apparatus requires only a radiation source,means of focusing the exposure radiation from the original onto theimaging sheet means to join the amazing sheet with the developer sheetand means for rupturing the encapsulate. Simplified means such as thiscan be used with the invention because development is essentially a dryprocess with the developer and chromogenic material reacting in only theinfinitesimal droplets of solvent encapsulated in the internal phase.Furthermore, the chromogenic material and the developer are on theimaging and developer sheets in the amounts (coverage) required forimaging, hence, the invention obviates the elaborate means required inmost prior photocopy systems for coating and metering the developingagent onto the imaging sheet in sufficient amounts.

The present invention is illustrated in more detail by the followingnon-limiting examples:

EXAMPLE 1 Ultraviolet Photosensitive Microcapsule Preparation (UFCapsules)

To 25 parts of a filtered solution prepared by dissolution of 5.0 partsof gum arabic (Celanese; grade A-13, gum arabic special) in 50.0 partsof distilled water was added with stirring 26.9 parts of a 17.1% (totalsolids) solution of isobutylene/maleic anhydride copolymer and sodiumhydroxide, prepared by addition of 5.44 parts of isobutylene/maleicanhydride copolymer (average molecular weight=1.0×10⁶) and 2 parts ofsodium hydroxide in 32.5 parts of distilled water with stirring andheating to 92° C. for 2 hours. Subsequently 38.3 parts of distilledwater was added and after heating to 60° C. the pH of the resultingmixture was adjusted to 4.0 (from an initial pH of 8.8) by theportionwise addition of 10% (V/V) aqueous sulfuric acid. Withmaintenance of the 60° C. temperature and constant stirring, 6.6 partsof urea and 0.8 parts of resorcinol were added and the pH of the mixturewas readjusted to 4.0 with 10% (V/V) aqueous sulfuric as previouslydescribed. The completed solution, hereafter referred to as the aqueousphase, was maintained at 60° C. for immediate use.

Preparation of the internal phase, hereafter known as the organic phase,proceeded as follows: in a mixture of 40.0 parts of trimethylolpropanetriacrylate (TMPTA) and 10.0 parts of methyl methacrylate (MMA) wasdissolved with stirring and heating to 90° C., 3.0 parts of the colorprecursor, 3-diethylamino-6-methyl-7-anilinofluoran. While allowing themixture to cool to 60° C., 2.5 parts of benzoin methyl ether and 1.0parts of 4,4'-bis(dimethylamino)benzophenone were added and the mixturewas allowed to stir until complete dissolution of these materials. Thecompleted organic phase was maintained at 60° C. for immediate use.

Preparation of the urea-formaldehyde microcapsules proceeded as follows:to a commercial Waring blender equipped with a speed control consistingof a variable voltage power supply (variable autotransformer; 0 to 140volt range) and preheated to 60° C. by means of a heated, forced airsupply was added the entire aqueous phase. With the blender operating at40 volts, the entire organic phase, also preheated to 60° C., wascarefully added in a thin continuous stream. With provisions made formaintenance of the internal temperature at 60° C., the blender wasoperated at 90 volts for 45 seconds to effect emulsification. Directlyafter this 45 second period, the power supply setting was reduced to 40volts, an aliquot was taken and the average particle size was determinedby visual examination of the emulsion under a microscope. The averageparticle size was 4.5 microns.

Following this determination, 18.4 parts of a 37% (W/V) aqueousformaldehyde, preheated to 60° C., were added in one portion. Afterblending for 2 hours the mixture was transferred to a heatable containerequipped with an efficient mechanical stirrer, the temperature wasmaintained at 60° C. and a solution of 0.6 parts of ammonium sulfate in12.2 parts of water was added with high speed stirring. After 1.0 hoursof stirring, the mechanical stirrer was removed, provision was made formagnetic stirring and the pH was adjusted to 9.0 (from an initial pH of3.2) by the portion-wise addition of 10% (W/V) aqueous sodium hydroxide.Microcapsule emulsion preparation was completed by the addition of 2.8parts of sodium bisulfite followed by an additional 10 minutes ofstirring.

Preparation of Light Sensitive Sheets from the Above MicrocapsulePreparation

A slurry consisting of 10 parts of the above light sensitivemicrocapsule and 10 parts of distilled water was coated on 80 lb. blackand white enamel paper stock using a #10 drawdown rod as the coatingdevice and the coated papers were dried briefly in a circulated hot airoven at 95° C. The resulting dry sheets were immediately useable orcould be stored for later use.

Preparation of Developer Sheet

To 218 parts of water were added with slow stirring 5.8 parts of a 50%aqueous suspension of styrene-butadiene latex, 40 parts of 10% aqueous1.5% ethylated starch, 17 parts of hydrated silica gel, 21 parts of zinccarbonate, 13 parts of 47% aqueous sodium silicate, 1 part sodiumhexa-meta-phosphate and 130 parts of Silton F-150 clay. After stirringat ambient temperature for 1 hour, the mixture was stabilized by theaddition of 0.1 part of 37% aqueous formaldehyde and coated upon 80 lb.black and white enamel paper stock using a #10 drawdown bar as thecoating device. The sheets were completed by brief drying in arecirculated hot air (95° C.) oven.

Reproduction of Images Using the Above Light Sensitive Sheets

The apparatus used in the reproduction of images using the lightsensitive sheets consisted of: a near UV light source (2, 15 wattF-15-T8-BLB black light bulbs), a positive photographic transparency, aplate glass cover plate and a calender stack capable of providing atleast 30 lb. per lineal inch crushing pressure. Images were reproducedin the following way: a light sensitive sheet was positioned with lightsensitive surface uppermost on a horizontal surface, the positivetransparency was superimposed upon this sheet, followed by the glasscover plate and the assembly was irradiated for periods of 1, 2, 3 and 4seconds by the above mentioned UV light source positioned parallel toand approximately 5 inches from the above assembly. Following exposure,the light sensitive sheet was placed against an image receiving anddeveloping sheet prepared as above.

The sheets were positioned such that the active layers of each were inintimate contact and the assembled sheets were calendered. Suchtreatment and separation of the sheets resulted in the production of areversed positive black image. Exposures of 1 and 2 seconds gave imagesof essentially similar quality, with good resolution and half-tonegradation. The 2 second exposure gave somewhat less transferred anddeveloped dye background. Exposures of 3 and 4 seconds gave lower imageintensity typical of over exposure.

EXAMPLE 2 Ultraviolet Photosensitive Microcapsule Preparation (UFCapsules)

An aqueous phase was prepared in exactly the same manner and proportionsas described in Example #1.

Preparation of an organic phase proceeded as follows: to 50.0 parts oftetraethylene glycol diacrylate (TEGDA) was added with heating to 90° C.and stirring 3.0 parts of the same color precursor mentioned inExample 1. After complete dissolution of the dye precursor the mixturewas allowed to cool to 60° C. and 2.5 parts of benzoin methyl ether and1.0 parts of bis-4,4'-(dimethylamino)benzophenone were addedsuccessively and the mixture was stirred at 60° C. until completedissolution occurred. The organic phase was maintained at 60° C. forimmediate use.

The preparation of the urea-formaldehyde capsules proceeded exactly asdescribed in Example 1, with the following important modification andobservation: after careful addition of the organic phase to the aqueousphase in the blender, the blender was operated at 90 volts for 60seconds instead of 45 seconds and the observed size of the emulsiondroplets was, on the average, 5.0 microns instead of 4.5 microns.Capsule preparation was completed exactly as described in Example 1.

Preparation of Light Sensitive Sheets from the Above MicrocapsulePreparation

A slurry consisting of 10 parts of the above microcapsule preparationand 10 parts distilled water was coated on 80 lb. black and white enamelpaper stock using a #10 drawdown rod as described in Example 1.Preparation of the light sensitive sheets was completed exactly asdescribed previously and the resulting light sensitive sheets wereimmediately useable or could be stored for later use.

Reproduction of Images Using the Above Light Sensitive Sheets

The apparatus used for image reproduction was exactly the same asdescribed in Example 1. Exposures of from 1 to 4 seconds resulted in nodeveloped image, however; exposures of 1 and 2 minutes gave high qualityblack image reproduction after development by calendering against thesame image receiving sheet as was used and described in Example 1.

Having described the invention, it is to be understood that theinvention is not limited to this precise process and product, and thatchanges may be made therein without departing from the scope of theinvention which is defined in the appended claims.

What is claimed is:
 1. A transfer imaging system in which images areformed by image-wise reaction of one or more chromogenic materials and adeveloper, said system comprising:an imaging sheet comprising a firstsubstrate, a chromogenic material, a photodepolymerizable compositionwhich undergoes a decrease in viscosity upon exposure to actinicradiation, a coating on one surface of said first substrate comprisingsaid chromogenic material and said photodepolymerizable composition,said photodepolymerizable composition being encapsulated in rupturablecapsules as an internal phase, and a developer sheet comprising a secondsubstrate and a developer material capable of reacting with saidchromogenic material to form an image on one surface of said substrate,wherein images are formed by image-wise exposing said coating to actinicradiation, and rupturing said capsules in the exposed areas with saidcoating in facial contact with said developer sheet such that saidinternal phase is image-wise released from said ruptured capsules andthere is image-wise transfer of said chromogenic material to saiddeveloper sheet and a patterned image-forming reaction occurs betweensaid chromogenic material and said developer material.
 2. The imagingsystem of claim 1 wherein said capsule is a microcapsule having adiscrete capsule wall.
 3. The imaging system of claim 2 wherein saidchromogenic material is encapsulated with said photodepolymerizablecomposition.
 4. The imaging system of claim 2 wherein saidphotodepolymerizable composition comprises a photoinitiator.
 5. Theimaging system of claim 4 wherein said chromogenic material is asubstantially colorless electron donating compound.
 6. The imagingsystem of claim 2 wherein said photodepolymerizable composition issensitive to ultraviolet, infrared, X-ray, electron beam, or visibleradiation.
 7. The imaging system of claim 2 wherein saidphotodepolymerizable composition is sensitive to ultraviolet radiation.8. The imaging system of claim 2 wherein said photodepolymerizablecomposition is sensitive to blue light having a wavelength in the rangefrom 380 to 480 nm.
 9. The imaging system of claim 2 wherein said systemincludes means for temporarily shielding said coating composition fromambient radiation such that said system can be handled in room light forat least a short period of time without interfering with theimage-forming capability of said system.
 10. The imaging system of claim5 wherein said chromogenic material is an oil soluble color former. 11.The imaging system of claim 2 wherein said capsule wall is formed by ahydrophilic material which transmits said actinic radiation.
 12. Theimaging system of claim 9 wherein said means for temporarily shieldingsaid coating composition from ambient radiation includes a yellowfugitive dye, said dye being present in a layer overlying said coatingcomposition.
 13. A transfer imaging process comprising:image-wiseexposing to actinic radiation an imaging sheet comprising a firstsubstrate and a coating composition of said substrate, said coatingcomposition including a chromogenic material and a photodepolymerizablecomposition which undergoes a decrease in viscosity upon exposure toactinic radiation, said photodepolymerizable composition beingencapsulated in rupturable capsules, rupturing capsules in the exposedareas, and transferring said chromogenic materials from the rupturedcapsules to a sheet carrying a developer material on one surface suchthat there is a patterned reaction between said developer material andsaid chromogenic material which produces an image.
 14. The process ofclaim 13 wherein said rupturable capsule is a microcapsule defined by adiscrete capsule wall.
 15. The process of claim 14 wherein saidimage-wise exposing is by transmission imaging.
 16. The process of claim14 wherein said image-wise exposing is by reflection imaging.
 17. Theprocess of claim 16 wherein said capsules are ruptured by applyingpressure to said imaging sheet and said developer sheet, said sheetsbeing superposed with said developer material facing on said coatingcomposition.
 18. The process of claim 17 wherein said actinic radiationis ultraviolet radiation, infrared radiation, visible light, x-ray, orion beam irradiation.
 19. The process of claim 18 wherein said actinicradiation is ultraviolet radiation or visible blue light having awavelength in the range 380 to 480 nm.